So he thinks he can take your 24th level character in a fight? Pretty impressive guy. Nah, let him harass you and start giving the DM messages. Tell the DM how you are starting to have flashbacks and you are having nightmares about your slavery. Repressed anger being brought out by the _betrayal_ of somebody you thought was your friend. In game, start allowing a random chance to lash out in blind rage. Finally, when your "firend" goes off on you one night, wait until you are on watch and he is asleep. In the middle of the night, on your watch, have him snap. Coup de Grace with your great axe, while raging and power attacking (if your DM will allow it). Immediately start screaming that the guards are down and everyone can escape. Slaughter the "friend" and break off into the woods, encouraging everyone else to run with you. Stop and attack a tree until it goes down. Yell that another guard is down and it is even easier to escape. Wash, rinse, repeat until you stop raging and come to your senses. You see, you are cracking under the pressure. You were willing to die to save him and now he treats you like this. It does things to people...
Just run it all by the DM ahead of time so he realizes you are playing it in-character. If he doesn't like the response, maybe the three of you should iron out the harassment his character is throwing your way.